The cBN sintered body has high hardness and excellent in thermal conductivity, so that it has been used as a cutting tool for machining a hardened steel or heat-resistant alloy. As a prior art of the cBN sintered body tool, there is a cBN sintered body tool having a cBN content of 40 to 80 vol % in which the cBN is bonded through a ceramics binder comprising a Ti compound which has a low affinity to an iron-group metal (excellent in thermal and chemical stability) (for example, see Non-Patent Literature 1.). In FIG. 1 of Non-Patent Literature 1, there are disclosed that in a hardened steel machining using a cBN sintered body tool, if a content of cBN is low, a wear amount is small (wear resistance becomes high) but fracture resistance is poor, to the contrary, if the content of cBN is high, fracture resistance is high but the wear amount is large (wear resistance is lowered). That is, it was difficult in the cBN sintered body tool to improve wear resistance and fracture resistance simultaneously.
As a method for improving wear resistance of the cBN sintered body tool, there is a method of covering a coating excellent in wear resistance on the surface of the tool. As the prior art of the coated cBN sintered body tool in which the coating layer is coated on the cBN sintered body, there is a composite high-hardness material for a hardened steel cutting tool in which a TiAlN film having an atomic ratio X of Ti/(Ti+Al) being 0.3≦X≦0.5 is coated on the surface of a substrate which comprises a CBN sintered body containing 20% by volume or more of cubic boron nitride (for example, see Patent Literature 1.). However, regarding the composite high-hardness material for a hardened steel cutting tool coated by the TiAlN film, there are problems that if the content of the cBN contained in the substrate is low, fracture resistance is lowered, to the contrary, if the content of the cBN contained in the substrate becomes high, adhesiveness between the TiAlN film and the substrate is lowered whereby the TiAlN film is peeled off, which causes lowering in wear resistance. That is, in the coated cBN sintered body tool, it was difficult to improve wear resistance and fracture resistance simultaneously.